[FEATURE] Add bytes conversion to NDArray

[rbyche]

Description

Add bytes conversion to NDArray. The newly added NDArray's 'asbytes' and 'from_buffer' are completely equivalent to numpy's 'tobytes' and 'frombuffer', respectively. These features make better use of NDArray.

Checklist

Essentials

• [x] PR's title starts with a category (e.g. [BUGFIX], [MODEL], [TUTORIAL], [FEATURE], [DOC], etc)
• [x] Changes are complete (i.e. I finished coding on this PR)
• [x] All changes have test coverage
• [x] Code is well-documented

Changes

• [x] Add 'asbytes' method to NDArray
• [x] Add 'from_buffer' function to NDArray

Comments

• If this change is a backward incompatible change, why must this change be made.
• Interesting edge cases to note here

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